The success of educational programs is often determined by the coincidence of the testing instruments with instructional procedures and program content rather than by the actual performance of adults and children in the classroom situation. Standardized achievement tests, which are the principal instruments used for assessing program effects, present particular disadvantages for open classroom models because of the sequence of skill development implied in the test format, the construction of items, and the content of the items. These instruments and others available do not tap the major objectives of open classroom programs. The roster of objectives for open educational programs include several in the areas of socialization and problem solving which are central to the dynamics of the program, but, at present, do not allow for the establishment of specific measures of program effects. A description of the interaction of elements within an open classroom model is presented as a total system in which the assessment of process assumes a more important function than assessment of products represented by the concept underlying standardized achievement tests. Dimensions which show promise for assessment of program effects in an open system are discussed. (Author)